Interest in heating thermoelectric generators with liquid fossil fuels was enhanced several years ago when an ultrasonic atomizer capable of atomizing liquid fuels into a mist of fine particles was developed. The art had previously desired generators heated with liquid fossil fuels.sup.1 but had been inhibited by deficiencies in traditional techniques for atomizing such fuels..sup.2 Ultrasonic atomizers gave promise of overcoming these deficiencies because of the low fuel pressures used in ultrasonic atomization, the very fine size of the atomized particles, and the compact size of the mist of atomized particles. Designs for thermoelectric generators using ultrasonic atomizers followed after the introduction of such atomizers; see paper CP 66-3 presented at the American Petroleum Institute Research Conference on Distillate Fuel Combustion for 1966 (API Publication No. 1705)(for suggestions of other burner assemblies generally intended for uses other than in thermoelectric generators see other papers in the series CP 66-1 through CP 66-6 of that publication, API publications for other years, and U.S. Pat. No. 3,275,059). FNT 1. For one reason, gaseous fuels such as propane, which are today generally used to heat commerical thermoelectric generators, require large, heavy, pressurized storage tanks. These tanks add expense to installation and operation of thermoelectric generators, and they conflict with the advantages of portability and small size offered by thermoelectric generators. Also, if the variety of liquid fossil fuels that are commercially available could be used to heat a thermoelectric generator, a flexibility in fuel selection would result that is desirable for many installations of thermoelectric generators. FNT 2. Some of the deficiencies in the traditional technique of forcing liquid fuel under pressure through a nozzle include: (a) the pressure-atomized spray of fuel is too large for the small combustion chambers desired in compact thermoelectric generators; (b) the pressure-atomized fuel particles are relatively large and require large supplies of air for combustion, meaning that unduly high percentages of the output of the generator are required to drive an air blower; (c) the small-diameter nozzle orifice necessary for low rates of fuel flow such as used in a thermoelectric generator is susceptible to clogging; and (d) the technique permits only limited adjustment of the amount of electricity generated or the variety of fuel used.
However, despite the prior suggestions for thermoelectric generators incorporating burner systems based on ultrasonic atomizers, and despite significant efforts based on those suggestions, no successful thermoelectric generator of this type has ever been produced until the present invention. None of the previous suggestions was able to satisfy the rather severe requirements for a burner system in a thermoelectric generator. A primary requirement leading to other requirements is that the burner system must be compact to make the generator compact. Yet the system must operate at a peak efficiency so as to maximize the efficiency of the generator. Further, the system must be capable of long, unattended operation, and the burning must be stable so as to provide a stable supply of heat distributed uniformly over the hot ends of the thermoelectric legs in the generator.
We have found that a prinicpal reason for the failure of the previous designs lies in the scheme provided in those designs for controlling the movement of fuel and air through the burner system. The prior suggestions have not provided a mixing of fuel and air that was rapid, thorough, and uniform enough; the mixture of fuel and air was not compact enough; and too large volumes of air were required. The failure of the burner systems previously suggested for thermoelectric generators--they have generally been incapable of long, stable, and trouble-free operation, and they have been inefficient in use of fuel and in use of generated electricity to power movement of air--may be traced directly to failure to properly control the movement of fuel and air through the burner system. Proper control of that movement of fuel and air is critical to providing long-lasting, efficient burner systems based on ultrasonic atomizers for use in thermoelectric generators.